1. Field of the Invention
This invention relates to a blade for a windmill, a windmill and a wind power generator, and especially a vertical type windmill, a blade for a windmill used for this windmill and a wind power generator using the vertical type windmill.
2. Background of the Art
There are vertical rotation axis type and horizontal rotation axis type windmills, and nowadays horizontal rotation type ones are mainly used for wind power generation. Horizontal rotation axis type windmills have an advantage of having a greater collection rate of wind energy than that of vertical rotation axis type windmills, however the rotation efficiency decreases unless the rotation axis and blades are opposed to the wind direction, and especially they have disadvantages of speed decrease occurred by difference of the wind direction due to elevation difference between the upper and lower blades and speed decrease due to rapid change of the wind direction (for example, twister).
On the other hand, vertical rotation axis type windmills (for example, referred to Patent Document 1) can rotate regardless of the wind direction, however they have a disadvantage that a blade on one side of the vertical rotation axis receives rotation force fully, but a blade on the other side receives resistance due to the headwind.    [Patent Document 1] Japanese Laid-Open Patent Publication No. 2001-132617